Reactivation of nitration reaction vessels



aiented Apr. l, 1941 were I 2,236,906 nnsc'rrva'rrou or marrow nusm'ron VESSELS Edward B. Hodge, Terra Hautc, Ind assignor to Commercial Solvents Corporation, Terre Haute, Ind., a corporation of Maryland No Drawing. Application May 6, 1939,

, a Serial No. 212,153

4 Claims. v(c1. 260-644) '1 My invention relates to the production of nitrohydrocarbons. More specifically, my invention relates to an improvement in the production of nitrohydrocarbons by the direct vapor phase nitration of saturated hydrocarbons.

The direct vapor phase nitration of saturated hydrocarbons is described in U. 8. Patent No. 1,967,667 of H. B. Hass et 8.1., U. 8. Patent 2,071,122 oi H.-B. Hass et al., and in co-pending application Serial No. 98,634 of H. B. Hass et a1. According to this process saturated hydrocarbons and nitric acid, or nitrogen dioxide, are contacted in a reaction vessel maintained at a sumciently high temperature to insure vapor phase conditions at the pressure employed. Although this reaction gives satisfactory initial yields and conversions, I have found that there is a tendency for these yields and conversions to drop 03 after continued operation. This eflect is similar to the deterioration or poisoning of 'a catalyst in a catalytic reaction,. but as there is no catalyst employed in the present case the expianation of this phenomenon is not clear. It appears, however, that a material which catalyzes undesired reactions tends to build up in the systern. This theory is supported by the fact that the phenomenon is encountered to different degrees in reaction vessels of different compositions, and also by the fact that the nitric acid is destroyed in the reaction even when the yield of nitrohydrocarbon has markedly dropped ofl. It should be understood, however, that my invention is not to beconstrued as related to any theoretical explanation of the above described phenomenon. Irrespective of the true explanation of this phenomenon I will refer to it herein for convenience as "deactivation of reaction vessel.

It has been found that reactors made of copper, aluminum, or iron, or of the ferrous alloys such as stainless iron or stainless steel, which are particularly suited for the construction of such apparatus, deactivate relatively easily, and that this deactivation is accelerated by contact of any liquid nitric acid with the interior surfacw of the reaction vessel. Although these reaction vessels become deactivated relatively slowly during use, it has been found that they may be rapidly deactivated by treatment of the interior surfaces of the vessel with liquid nitric acid. When the reaction vessel has been deac'ti vated either by continued use or by accelerated treatment with liquid nitric acid, it is unsuitable for further economic operation of the nitration reaction. When the vessel is in this condition it is impossible to reactivate it by simple 7 treatments, such as thorough washing'with water or heating to a temperature substantially above the reaction temperature. However, in copending application Serial No; 272,152 of E. B. Hodge and L. C. Swallen, it is shown that the deactivated reaction vessels may be reactivated by treatment with a compound of a metal of the alkali or alkaline earth groups.

I have now found that a number of other metallic compounds are suitable reactivating agents for this purpose. The reactivating agents of my present invention comprise copper sulfate, silver nitrate, beryllium sulfate, magnesium nitrate, magnesium sulfite, magnesium chloride, zinc nitrate, zinc chloride, cadmium nitrate, cadmium acetate, aluminum sulfate, thallium nitrate, titanium dioxide, cerium nitrate, thorium nitrate, stannous chloride, lead oxide, lead nitrate, lead chloride, arsenic trioxide, ortho arsenic acid, an-

timony trloxide, molybdenum sesquioxide, molybdic acid, and uranyl nitrate. Any of these compounds may suitably be used forthe reactivation treatment, but the reactivating powers of the various compounds will be found to differ to some extent. In general. it may be said that'among the compounds listed above, the compounds of the metals of the second, third, and fourth groups of the periodic system arethe most active. Among these I prefer to utilize magnesium chloride, aluminum sulfate, and cerium nitrate, but it is tov be understood that my invention is not to be limited to the use of these particular compounds. Beneflcial results may be secured by the use of any of the compounds listed above, and simple preliminary experiments will enable one skilled in the art to choose a suitably active material for use with any type of reaction vessel, or any combinatio'n of operating conditions.

In carrying out my invention it is necessary merely to treat the interior surfaces of the reaction vessel with a solution or suspension of one of the compounds enumerated above, in accordance with the procedure of co-pending application Serial No. 272,152, previously referred to. When the reaction vessel becomes deactivated it should preferably be thoroughly washed with water and filled with a solution of the desired reactivating agent. The concentration of the solution of re'activating agent and the time of treatment are not critical, but I prefer in most cases to utilize a solution of approximately 10% to 30% concentration and to allow the solution to remain in the vessel for a period of 5 to 10 minutes. In the case of relatively insolube materials .a suspension of equivalent concentration reactivation. depends to some extent'upon the activity of the particular reactivating agent used, less heat treatment generally being required for the more active reactivating agents than for the less active agents. A temperature in excess of 225 C. is usually required even for the most active reactivating agents, and less active compounds may reqmre temperatures very' much higher. I prefer to employ temperatures at least as high as 200 0., and I have successfully reactivated at temperatures as high as 900' C., or even higher. The more active compounds will reactivate successfully within the range 350-600 0. Since this constitutes a useful temperature range for the nitration reaction, the reactivation mayv be completed, after treating with the solution oifv the reactivating agent, simply by placing the vessel back in operation in the nitration reaction. From the standpoint of simplicity of operation, I prefer to utilize this procedure.

If a separate heat treatment is utilized, rather than relying upon the reaction temperature of the nitration reaction to complete the reactivation, the vessel may be washed, if desired, after the heat treatment, and before use in the nitration reaction. This procedure is unnecessary, however, and I generally prefer to employ the vessel directly, without further washing. In the absence of such washing, incomplete reactivation due to insufflcient heat treatment will tend to be overcome by the additional heating encountered during use in the nitration reaction. In the usual operation of my process, therefore, it is unnecessary to consider the time factor for the heat treatment. If, however, a separate heat treatment is employed, and the vessel is then washed prior to use, it becomes necessary to ensure a minimum duration of the heat treatment sumcient to effect reactivation. This time will tend to differ somewhat with the temperature used, and with the activity of the reactivating agent, In general, I prefer to maintain the vessel at the reactivating temperature for at least 5 minutes, and preferably for -60 minutes. In any particular case, however, preliminary experiments will indicate the minimum time necessary for optimum reactivation at the temperature involved. I

My invention will now be illustrated by specific examples illustrating the reactivating effect of various compounds of the group defined above.

Example I A stainless iron reaction tube of 80 ml. capacity was deactivated by filling with 8 N nitric acid,

reduce the yield of the nitrohydrocarbons to approximately milliliters per hour under the reaction conditions utilized for the test. The reaction tube was then blown out with air, replaced in the apparatus, and a test run was made to determine the yield of nitrohydrocarbons per hour with the deactivated tube. The reactants were and allowing this to remain for a few minutes to secure a degree of deactivation sufiicient to' assaooo propane and nitric acid, and the following reaction conditions were maintained:

Vaporizer temperature 220-30 C,

Yield of nitrohydrocarbons before reactivation Yield of nitrohydrocarbonsafter reactivation M1. per hour M7. hour so '53 Example II The procedure of Example I was followed with the exception that the reaction tube was deactivated only to a point corresponding to a yield of nitrohydrocarbon's of approximately milliliters per hour and magnesium nitrate was used as the reactivating agent. The following results were secured:

Yield of nitrohydrocarbons before reactivation Yield of nitrohydrocarbons alter reactivation M. per hour MI. per hour 97 200 Example III The procedure of Examples I and II was followed utilizing various degrees of deactivation and various reactivating agents. The increase in yield secured with each reactivating agent is shown in the table below:

. Increase in Reactivating agent id of nitroydrocarbons M. boar AgNO; G) Zn(N0 H), Cd N0 b5 Tl( Os): 0o Ce(NO- 4 47 Pb(NOr)| 68 U0|(NO;)| 37 As may be seen from Examples I and II reactivation may be secured irrespective of the stage of deactivation of the reaction vessel. It is thus possible to reactivate at any time when the yield drops sufficiently to warrant stopping the process for the period necessary to reactivate. In view of the fact that the reactivation procedure is extremely simple, and a very short time is required, it will usually be found to be desirable to reactivate when the degree of deactivation secured is even less than that of Example II.

The following example illustrates reactivation when operating the nitration reaction at atmospheric pressure rather than at the elevated pres sure employed in the preceding examples:

Example IV Stainless steel reaction tubes of 80 ml. capwity were deactivated as in the preceding examples,

tested for yield'in the deactivated state, reacti-.

vated with the agents noted below, and again tested for yield. The yield tests were made under The yields before and after reactivation are shown in the table below:

Yield before Yield after Reactivatmg agent reactivating reactivatiug Ml. per Mb ,Ml. per M50 06(NO )4 M cu' o 25 5!:(304): 5 24 It will be obvious to those skilled in the art that the procedure of the above examples may be modified in numerous respects without departing from the scope of my invention. Equivalent compounds may be utilized in place of the particular compounds specified in the examples, or a combination of two or more reactivating agents may be used if desired. Instead of employing an aqueous solution or suspension of the reactivating agent, other solvents may be employed, or the interior of the reaction vessel may suitably be coated with the solid material in a fused state. In-general, it may be said that the use of any such modifications, and the use of any equivalents which would naturally occur to one skilled in the art, are included within the scope of my invention.

This application is a continuation-in-part of my co-pending application, Ser. No. 126,641, filed February-19, 1937.

My invention now having been described, what I claim is: V

1. The process of reactivating a reaction vessel which has become deactivated during vapor Phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of such reaction vessel, at a temperature above 225 C., with a metal salt selected from the group consisting of copper sulfate, silver nitrate, beryllium sulfate, magnesium nitrate, magnesium sulflte, magnesium chloride, zinc nitrate, zinc chloride, cadmium nitrate, cadmium acetate, aluminum sulfate, thallium nitrate, cerium nitrate, thorium nitrate, stannous chloride, lead nitrate; lead chloride, and uranyl nitrate.

2. The process of reactivating a reaction vessel which has become deactivated during vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of such reaction vessel, at a temperature of 350- 600 0., with cerium nitrate.

3. The process of reactivating a reaction vessel which has become deactivated during vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of such reaction vessel, at a temperature of 350- 600 C.; with magnesium chloride.

4. The process of reactivating a reaction vessel which has become deactivated during vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of such reaction vessel, at a temperature of 350- 600 C., with aluminum sulfate.

- EDWARD B. HODGE. 

